Summary The Advanced Tissue Pathology and Imaging (ATPI) Core provides a wide spectrum of histopathology and microscopy services to meet the growing needs of diabetes researchers at Columbia University and affiliated institutions. Originally organized as a histopathology laboratory, the Core has evolved to meet the growing demands of DRC members by adding advanced microscopy services. The services of this Core continue to include high quality basic histological and microscopy services, and have been expanded to accommodate the changing and growing needs of DRC users and to incorporate newly developed reagents and technologies. Following the departure of former Core Director Dr. Sussel to lead the Barbara Davis Center at the University of Colorado, the Core has been ably led by Dr. Paul Harris, an internationally known investigator in islet imaging and cell biology. During the past cycle, the ATPI Core has processed 21,312 tissue samples, cut 248,342 sections and performed 21,381 immunohistochemical stains, including 4,862 samples by immunofluorescence. These services were provided to 30 DRC members supported by 84 grants. The resultant data have contributed to 12 new grants, and 93 Core-supported publications (61 as primary, 32 as secondary Core) (Overall Tables D and F, respectively). The Core plans to continue to provide advanced histophenotyping capabilities to the thriving Columbia University diabetes research community. To this end, the Core integrates its operation with that of the other DRC Core facilities, to maintain an investigator- oriented approach to service and development, to implement and sustain effective business practices, and to assist the DRC in its overall mission to advance our understanding of diabetes and its complications and develop new treatments for these conditions.